The present invention relates to a method and device for determining varying acceleration or deceleration of an object, particularly acceleration or deceleration of an automotive vehicle wheel for use as part of an anti-skid control in a brake control system. More specificaly, the invention relates to a method and device for the acceleration and deceleration of an automotive vehicle wheel. The device measures the pulse period of a wheel rotation speed sensor signal by measuring the time interval over which suitable numbers of sensor signal pulses are received.
In accordance with automotive anti-skid brake control systems, it is necessary to effectively and accurately determine acceleration or deceleration of at least one automotive vehicle wheel. In various anti-skid control systems, a typical skid-control procedure is to determine a target wheel rotation speed based on the acceleration and/or deceleration thereof, and to control the actual wheel rotation speed to correspond with the target wheel rotation speed. The acceleration and/or deceleration of a wheel is determined by differentiation of a difference between wheel rotational speeds during a period and an immediately preceding period. Such an anti-skid control technique requires the accurate and rapid determination of the acceleration and/or deceleration .alpha. over a significant range of vehicle speed. The acceleration and/or deceleration of the vehicle is generally obtained from the following equation in which the intervals between successive pulses of a sensor signal fed from the wheel rotation speed sensor are denoted as Tn-1, Tn, Tn+1 . . . : ##EQU1##
In such a conventional system it is only possible to determine the difference in pulse period between each successive pulses. This creates a problem in that when the wheels, that rotate at a high velocity, the difference between successive pulse periods approaches zero which lowers the resolution of the calculated value of the acceleration and/or deceleration rate. This disadvantage is clearly illustrated in the following example.
If the brakes are applied to a vehicle moving at a speed of 100 km/h to decelerate at a rate of 0.1 G and assuming the pulse period of the wheel rotation speed sensor signal is measured with reference to a 1 .mu.s clock pulse, the pulse period of both the first and second sensor signal pulses Tn-1 and Tn will be 522 .mu.s. Thus, it is practically impossible to measure the difference between successive pulse periods. In order to eliminate the foregoing disadvantage of the conventional system, the system can be modified to measure the difference between successive intervals over which a predetermined number of pulses of the wheel rotation speed sensor are received. For example, in the above case of acceleration of 0.1 G from speed of 100 km/h with a 1 .mu.s clock pulse, the deceleration rate .alpha. can be adequately resolved by measuring the periods of successive of pulses. Note that under the same conditions as those specified above, except starting from the relatively low speed of 10 km/h, the period of a group of 8 pulses would be on the order of 40 ms. Therefore, according to this procedure, the difference between the pulse periods of adjacent groups of vehicle speed sensor pulses, which operating at high speeds, can be satisfactorily resolved. However, for determining the difference of the pulse periods are relatively low speeds the pulse grouping technique involves a rather long period of time (e.g. yoms at 10 km/h) which makes it difficult to effectively employ anti-skid brake control techniques.
Therefore, in conventional systems for determining acceleration and/or deceleration of wheel rotation, it is desirable to provide a system or device capable of accurately determining changes in vehicle speed sensor pulse group period and of minimizing the period of time need for determining those changes.